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Fourier transform (FT)-Raman combined with partial least squares regression (PLS-R) calibration models allows the accurate monitoring of solids content, copolymer composition, and free amounts of monomers in starved semi-batch emulsion copolymerizations. The calibration models remain valid as long as the spectrometer and the measuring conditions are unchanged. Unfortunately, maintenance and/or repairing of the spectrometer result in changes in the relative intensities of the peaks of the Raman spectrum, reducing the performance of the calibration models. Therefore, a strategy for the up-date of the PLS-R calibration models is needed. Strategies for calibration model maintenance were assessed, and we found that the best strategy was to build a new model composed of the old PLS-R model plus a PLS-R model able to account for the model mismatch of the old model.

A high solids content n-butyl acrylate/methyl methacrylate emulsion copolymerization process carried out under starved semi-batch conditions was for the first time monitored on-line by means of Fourier transform (FT)-Raman spectroscopy. Partial least squares regression was employed to build calibration models that allowed relating the spectra with solids content (overall conversion), free amounts of both n-butyl acrylate (n-BA) and methyl methacrylate (MMA), and cumulative copolymer composition. In spite of the heterogeneous nature of the polymerization, the similarities of the spectra for MMA, n-BA, and for the copolymer, and the low monomer concentrations in the reactor, the FT-Raman spectroscopy has been shown to be a suitable noninvasive sensor to accurately monitor the process. Therefore, it is well suited for on-line control of all-acrylic polymerization systems.

Fourier Transform Raman spectroscopy was used as an on-line sensor in order to monitor high solids content (50 wt%) n-BA/MMA emulsion copolymerization reactions. Due to the similarity of the chemical structure of the monomers, no separate bands could be detected for each monomer, and therefore a multivariate calibration technique was required (Partial Least Squares Regression, PLSR). Using experimental data from several semi-batch reactions independent PLSR models were built for the solids content, cumulative copolymer composition and unreacted amounts of n-BA and MMA. Those models were experimentally validated by monitoring reactions not used for calibration. It is demonstrated that FT-Raman spectroscopy can be successfully applied to on-line monitor emulsion polymerization reactors. This technique also shows a high potential for process control purposes because independent information about several molecular properties can be obtained from a single apparatus.

Fourier Transform Raman spectroscopy was used as an on‐line sensor in order to monitor high solids content (50 wt%) n‐BA/MMA emulsion copolymerization reactions. Due to the similarity of the chemical structure of the monomers, no separate bands could be detected for each monomer, and therefore a multivariate calibration technique was required (Partial Least Squares Regression, PLSR). Using experimental data from several semi‐batch reactions independent PLSR models were built for the solids content, cumulative copolymer composition and unreacted amounts of n‐BA and MMA. Those models were experimentally validated by monitoring reactions not used for calibration. It is demonstrated that FT‐Raman spectroscopy can be successfully applied to on‐line monitor emulsion polymerization reactors. This technique also shows a high potential for process control purposes because independent information about several molecular properties can be obtained from a single apparatus.

Average particle sizes and particle size distributions (PSD) were measured using four different commercial techniques for standard polystyrene latexes in the submicron range, dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), disk centrifuge photosedimentometry (DCP) and transmission electron microscope (TEM). Both monodisperse latexes and broad particle size distribution latexes (obtained by mixing two or three monodisperse standards) were used in each equipment. It was found that for monodisperse latexes, DLS, CHDF and DCP gave similar measurements of particle size, which were also comparable to the particle sizes measured by TEM and reported by the supplier of the standard latexes. However, with the lowest particle size standard (39 nm), both DLS and CHDF gave larger particle size values, whereas with DCP, reasonable agreement with the measured size was obtained only when extremely long centrifugation times (at least 6 h) were used. For latexes having bimodal and trimodal distributions, both CHDF and DCP were able to reproduce the entire distribution, providing relatively accurate values for the average size of each mode and also the relative masses of each population of particles. However, the analysis time required by CHDF was shorter than by DCP, but the broadness of the peak was better captured by DCP than CHDF, which always provided broader peaks. DLS failed in most cases when measuring the broad size populations when the size ratio was greater than 2 : 1.